JP7347454B2 - Negative electrode active material layer - Google Patents

Description

The present disclosure relates to a negative electrode active material layer used in an all-solid-state battery.

All-solid-state batteries are batteries that have a solid electrolyte layer between a positive electrode active material layer and a negative electrode active material layer, and have simpler safety devices than liquid-based batteries that have an electrolyte containing a flammable organic solvent. It has the advantage of being easy to measure.

Lithium titanate is known as a negative electrode active material. For example, Patent Document 1 discloses an all-solid-state battery using a lithium titanate sintered body for the positive electrode or the negative electrode. Furthermore, Patent Document 2 discloses an all-solid-state battery including a negative electrode active material layer including a first layer and a second layer, the second layer containing lithium titanate. Further, although the technology is not related to all-solid-state batteries, Patent Document 3 discloses an electrode group in which the negative electrode active material layer contains a titanium-containing oxide.

Japanese Patent Application Publication No. 2015-185337 Japanese Patent Application Publication No. 2020-174004 JP2019-053946A

In lithium titanate, as will be described later, the plateau region occupies a large proportion of the charge/discharge curve. Therefore, when lithium titanate is used as the negative electrode active material, the electrode reaction tends to be biased in the thickness direction of the negative electrode active material layer, and as a result, the resistance tends to increase.

The present disclosure has been made in view of the above circumstances, and its main purpose is to provide a negative electrode active material layer with low resistance.

In order to solve the above problems, in the present disclosure, a negative electrode active material layer used in an all-solid-state battery includes a first negative electrode active material and a second negative electrode active material, and the first negative electrode active material is The second negative electrode active material is lithium titanate, and the discharge capacity at a potential of 1.0V (vsLi ⁺ /Li) or more and 2.0V (vsLi ⁺ /Li) or less is 100% discharge capacity, and the 100% discharge capacity is 100% discharge capacity. If the average potential at the capacity of 0% or more and 50% or less of the capacity is _P1 , and the average potential at the capacity of 50% or more and 100% or less of the 100% discharge capacity is _{P2, then the above P 2 and} the above P ₁ Provided is a negative electrode active material layer, wherein the difference between the negative electrode active material and do.

According to the present disclosure, a specific second negative electrode active material is used together with the first negative electrode active material which is lithium titanate, and furthermore, since the proportion of the first negative electrode active material is at least a predetermined value, the resistance is low. It can be used as a negative electrode active material layer.

In the above disclosure, the second negative electrode active material may have a discharge capacity of 100 mAh/g or more at a potential of 1.4 V (vsLi ⁺ /Li) or more and 2.0 V (vsLi ⁺ /Li) or less.

In the above disclosure, the second negative electrode active material may be at least one of niobium titanium oxide and niobium tungsten oxide.

In the above disclosure, the ratio of the first negative electrode active material to the total of the first negative electrode active material and the second negative electrode active material may be 90% by volume or less.

The present disclosure also provides an all-solid-state battery including a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, The present invention provides an all-solid-state battery in which the negative electrode active material layer is the negative electrode active material layer described above.

According to the present disclosure, since it has the above-described negative electrode active material layer, it is possible to provide an all-solid-state battery with low resistance.

The present disclosure has the advantage of being able to provide a negative electrode active material layer with low resistance.

This is a charge/discharge curve of a half cell using LTO as a working electrode and Li foil as a counter electrode. FIG. 3 is a schematic cross-sectional view showing a state change depending on the charging state of a negative electrode active material layer containing LTO. This is a charge/discharge curve of a half cell using TNO for the working electrode and Li foil for the counter electrode. 1 is a schematic cross-sectional view illustrating an all-solid-state battery according to the present disclosure. These are the results of resistance measurements for all solid-state batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 3.

Hereinafter, the negative electrode active material layer and the all-solid-state battery in the present disclosure will be described in detail.

A. Negative Electrode Active Material Layer The negative electrode active material layer in the present disclosure is used in an all-solid-state battery and contains a first negative electrode active material and a second negative electrode active material. Moreover, the negative electrode active material layer contains a first negative electrode active material and a second negative electrode active material. The first negative electrode active material is lithium titanate. The second negative electrode active material has a discharge capacity of 1.0V (vsLi ⁺ /Li) or more and 2.0V (vsLi ⁺ /Li) or less as 100% discharge capacity, and a region of 0% or more and 50% or less of the 100% discharge capacity. When _{the average potential in the range of 50% to 100% of the 100% discharge capacity is P 1, the difference between P 2 and P 1} is 0.1 V or more. Furthermore, in the negative electrode active material layer, the ratio of the first negative electrode active material to the total of the first negative electrode active material and the second negative electrode active material is 40% by volume or more.

According to the present disclosure, a specific second negative electrode active material is used together with the first negative electrode active material which is lithium titanate, and furthermore, since the proportion of the first negative electrode active material is at least a predetermined value, the resistance is low. It can be used as a negative electrode active material layer.

Lithium titanate has advantages such as not undergoing expansion and contraction due to charging and discharging, high chemical stability because it is an oxide, and good electronic conductivity in a charged state. On the other hand, in the case of lithium titanate, the plateau region occupies a large proportion of the charge/discharge curve. FIG. 1 is a charge/discharge curve of a half cell using Li ₄ Ti ₅ O ₁₂ (LTO) for the working electrode and Li foil for the counter electrode. As shown in FIG. 1, in LTO, the plateau region occupies a large proportion both during Li insertion (during charging in an all-solid-state battery) and during Li desorption (during discharging in an all-solid-state battery). Note that the potential of LTO decreases when Li is inserted (during charging in an all-solid-state battery), and increases when Li is desorbed (during discharging in an all-solid-state battery).

If the plateau region occupies a large proportion of the charge/discharge curve, the electrode reaction tends to be biased in the thickness direction of the negative electrode active material layer. FIG. 2 is a schematic cross-sectional view showing a state change depending on the charging state of a negative electrode active material layer containing Li ₄ Ti ₅ O ₁₂ (LTO). First, the all-solid-state battery shown in FIG. 2(a) has a negative electrode active material layer (AN), a solid electrolyte layer (SE), and a positive electrode active material layer (CA) in this order along the thickness direction. As shown in FIG. 2A, when the SOC (State of Charge) is 0%, the negative electrode active material layer (AN) has a uniform color in the thickness direction.

Next, as shown in FIG. 2(b), when the SOC is 50%, the color becomes darker in the region of the negative electrode active material layer (AN) on the solid electrolyte layer (SE) side. This indicates that Li was inserted into the LTO located on the SE side. On the other hand, when the SOC is 50%, in the region of the negative electrode active material layer (AN) on the opposite side from the solid electrolyte layer (SE), the color tone is maintained to be similar to that in FIG. 2(a). This indicates that Li is not inserted into the LTO located on the opposite side of the SE. Next, as shown in FIG. 2C, when the SOC is 100%, the negative electrode active material layer (AN) has a uniform dark color in the thickness direction. This indicates that Li was inserted into the entire LTO contained in the negative electrode active material layer (AN).

Next, when discharging from SOC 100% to SOC 50%, the color becomes lighter in the area of the negative electrode active material layer (AN) on the solid electrolyte layer (SE) side, as shown in FIG. 2(d). This indicates that Li was desorbed from LTO located on the SE side. On the other hand, when the SOC is 50%, in the region of the negative electrode active material layer (AN) on the opposite side from the solid electrolyte layer (SE), the color tone is maintained at the same level as in FIG. 2(c). This indicates that Li is not desorbed from LTO located on the opposite side of SE.

As shown in FIGS. 2(a) to 2(d), the reaction between the negative electrode active material (LTO) and Li tends to occur in the region of the negative electrode active material layer (AN) near the solid electrolyte layer (SE), and This is less likely to occur in the region of the negative electrode active material layer (AN) that is far from the layer (SE). Therefore, when the SOC is low, the influence of the ion conduction resistance in the thickness direction is small, but as the SOC becomes high, the influence of the ion conduction resistance in the thickness direction becomes large. As a result, electrode reactions tend to be biased in the thickness direction of the negative electrode active material layer.

In contrast, in the present disclosure, together with the first negative electrode active material (lithium titanate), a second negative electrode active material (for example, niobium titanium oxide) in which the plateau region occupies a smaller proportion than the first negative electrode active material is used. FIG. 3 is a charge/discharge curve of a half cell using TiNb ₂ O ₇ (TNO) for the working electrode and Li foil for the counter electrode.

As shown in FIG. 3, TNO has a smaller proportion of plateau regions than LTO. Therefore, in the initial stage of Li insertion (charging in an all-solid-state battery), Li is inserted into TNO at a higher potential than LTO. As a result, in the region of the negative electrode active material layer (AN) far from the solid electrolyte layer (SE), TNO reacts faster than LTO, and can alleviate the bias in electrode reaction in the thickness direction. As a result, resistance during charging can be reduced. Furthermore, in the initial stage of Li desorption (during discharge in an all-solid-state battery), Li is desorbed from TNO at a lower potential than LTO. As a result, in the region of the negative electrode active material layer (AN) far from the solid electrolyte layer (SE), TNO reacts faster than LTO, and can alleviate the bias in electrode reaction in the thickness direction. As a result, resistance during discharge can be reduced. Thus, in the present disclosure, by using a specific second negative electrode active material together with the first negative electrode active material which is lithium titanate, a negative electrode active material layer with low resistance can be obtained.

The negative electrode active material layer in the present disclosure contains at least a first negative electrode active material and a second negative electrode active material as negative electrode active materials. The negative electrode active material layer may further contain at least one of a solid electrolyte, a conductive material, and a binder.

1. Second Negative Electrode Active Material First, the second negative electrode active material will be explained. The second negative electrode active material has a discharge capacity at a potential of 1.0V (vsLi ⁺ /Li) or more and 2.0V (vsLi ⁺ /Li) or less as 100% discharge capacity, and 0% or more and 50% or less of the 100% discharge capacity. When _the average potential _{at a} capacity _of It is. Note that since the potential of the second negative electrode active material in an all-solid-state battery increases due to discharge, P ₂ is usually larger than P ₁ .

P ₁ and P ₂ can be determined by the following method. First, a half cell having a working electrode containing a second negative electrode active material, a solid electrolyte layer, and a counter electrode made of Li foil is prepared. Note that the working electrode may contain at least one of a solid electrolyte and a conductive material, if necessary. Next, constant current discharge is performed on the half cell at 1/10 C to insert Li in an amount corresponding to 100% SOC into the second negative electrode active material. Thereafter, constant current charging is performed at 1/10 C to remove Li from the second negative electrode active material. At this time, the capacity at a potential of 1.0 V (vsLi ⁺ /Li) or more and 2.0 V (vsLi ⁺ /Li) or less is measured to determine the 100% discharge capacity. Next, from the Li desorption curve, the average potential P ₁ at a capacity of 0% to 50% at 100% discharge capacity and the average potential P ₂ at a capacity of 50% to 100% at 100% discharge capacity are calculated. demand.

The difference between P ₂ and P ₁ may be 0.2V or more, 0.3V or more, or 0.4V or more. Note that the difference between P ₂ and P ₁ in the TNO shown in FIG. 3 is 0.3V. Further, P ₁ is preferably lower than the discharge reaction potential (plateau potential) of the first negative electrode active material. P ₁ may be, for example, smaller than 1.5V (vsLi ⁺ /Li) and not more than 1.45V (vsLi ⁺ /Li). Further, P ₂ may be higher than the discharge reaction potential (plateau potential) of the first negative electrode active material. P ₂ is, for example, greater than 1.5V (vsLi ⁺ /Li), and may be greater than or equal to 1.55V (vsLi ⁺ /Li).

In addition, the second negative electrode active material has a charging capacity at a potential of 2.0 V (vsLi ⁺ /Li) or lower and 1.0 V (vsLi ⁺ /Li) or higher as 100% charging capacity, and 0% or more of 100% charging capacity 50 % or less capacity is _P3 , and when the average potential at 100% charged capacity is 50% or more and 100% or less is _P4 , the difference between _P3 and _P4 is 0.1V or more. It may be. Note that since the potential of the second negative electrode active material in an all-solid-state battery decreases due to charging, P ₃ is usually larger than P ₄ .

P ₃ and P ₄ can be determined by the following method. That is, a half cell is prepared in the same manner as above, and constant current discharge is performed at 1/10 C to insert Li into the second negative electrode active material. At this time, the capacity at a potential of 2.0 V (vsLi ⁺ /Li) or lower and 1.0 V (vsLi ⁺ /Li) or higher is measured to determine the 100% charge capacity. Next, from the Li insertion curve, calculate the average potential P ₃ at the capacity between 0% and 50% of the 100% charged capacity, and the average potential P ₄ at the capacity between 50% and 100% at the 100% charged capacity. .

The difference between P ₃ and P ₄ may be 0.2V or more, 0.3V or more, or 0.4V or more. Further, P ₃ is preferably higher than the charging reaction potential (plateau potential) of the first negative electrode active material. P ₃ is, for example, greater than 1.5V (vsLi ⁺ /Li), and may be greater than or equal to 1.55V (vsLi ⁺ /Li). P ₄ may be lower than the charging reaction potential (plateau potential) of the first negative electrode active material. P ₄ may be, for example, smaller than 1.5V (vsLi ⁺ /Li) and not more than 1.45V (vsLi ⁺ /Li).

The second negative electrode active material has a discharge capacity of, for example, 100 mAh/g or more at a potential of 1.4 V (vsLi ⁺ /Li) or more and 2.0 V (vsLi ⁺ /Li) or less. This discharge capacity can be determined by the following method. That is, a half cell is prepared in the same manner as above, and an amount of Li corresponding to 100% SOC is inserted into the second negative electrode active material at 1/10C. Thereafter, constant current charging is performed at 1/10 C to remove Li from the second negative electrode active material. At this time, the capacity at a potential of 1.4 V (vsLi ⁺ /Li) or more and 2.0 V (vsLi ⁺ /Li) or less is measured to determine the discharge capacity. The second negative electrode active material may have a discharge capacity of 120 mAh/g or more, or 140 mAh/g or more at a potential of 1.4 V (vs Li ⁺ /Li) or more and 2.0 V (vs Li ⁺ /Li) or less. It's okay.

The second negative electrode active material may have a charging capacity of 100 mAh/g or more at a potential of 2.0 V (vsLi ⁺ /Li) or lower and 1.4 V (vsLi ⁺ /Li) or higher. This charging capacity can be determined by the following method. That is, a half cell is prepared in the same manner as above, and constant current discharge is performed at 1/10 C to insert Li into the second negative electrode active material. At this time, the capacitance at a potential of 2.0 V (vsLi ⁺ /Li) or lower and 1.4 V (vsLi ⁺ /Li) or higher is measured to determine the charge capacity. The second negative electrode active material may have a charging capacity of 120 mAh/g or more, or 140 mAh/g or more at a potential of 2.0 V (vs Li ⁺ /Li) or less and 1.4 V (vs Li ⁺ /Li) or more. It's okay.

The discharge reaction potential and charge reaction potential of the second negative electrode active material are not particularly limited, but are each, for example, 1.0 V (vsLi ⁺ /Li) or more and 2.0V (vsLi ⁺ /Li) or less.

The second negative electrode active material preferably contains a metal element and an oxygen element, that is, it is a metal oxide. This is because metal oxides have high chemical stability. Examples of the metal elements contained in the metal oxide include Nb, Ti, and W. The metal oxide may contain only one kind of the above-mentioned metal element, or may contain two or more kinds.

An example of the second negative electrode active material is niobium titanium oxide. Niobium titanium oxide is a compound containing Nb, Ti and O. Examples of the niobium titanium oxide include TiNb ₂ O ₇ and Ti ₂ Nb ₁₀ O ₂₉ . Further, another example of the second negative electrode active material is niobium tungsten oxide. Niobium tungsten oxide is a compound containing Nb, W and O. Examples of niobium tungsten oxide include Nb ₂ WO ₈ , Nb ₂ W ₁₅ O ₅₀ , Nb ₄ W ₇ O ₃₁ , Nb ₈ W ₉ O ₄₇ , Nb ₁₄ W ₃ O ₄₄ , Nb ₁₆ W ₅ O ₅₅ , Nb ₁₈ W ₁₆ O ₉₃ is mentioned.

The average particle diameter (D ₅₀ ) of the second negative electrode active material is, for example, 10 nm or more, and may be 100 nm or more. On the other hand, the average particle diameter (D ₅₀ ) of the second negative electrode active material is, for example, 50 μm or less, and may be 20 μm or less. The average particle diameter (D ₅₀ ) can be calculated, for example, by measurement using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM).

2. First Negative Electrode Active Material Next, the first negative electrode active material will be explained. The first negative electrode active material is lithium titanate. Lithium titanate is a compound containing Li, Ti, and O.

The first negative electrode active material has a discharge capacity at a potential of 1.0V (vsLi ⁺ /Li) or more and 2.0V (vsLi ⁺ /Li) or less as 100% discharge capacity, and 0% or more and 50% or less of the 100% discharge capacity. The difference between P'2 and _P'1 is less _than 0.1V, where _P'1 is _the average potential at a capacity of It may be. P _{′ 1} and P _{′ 2} can be determined in the same manner as P ₁ and P ₂ in the second negative electrode active material described above.

The first negative electrode active material has a charging capacity at a potential of 2.0V (vsLi ⁺ /Li) or lower and 1.0V (vsLi ⁺ /Li) or higher as 100% charging capacity, and 0% or more and 50% or less of the 100% charging capacity. When the average potential at a capacity of 100% is _P'3 , and the average potential at a capacity of 50% to 100% of a 100% charged capacity is _P'4 , the difference between _P'3 and _P'4 is 0.1V. It may be less than _P'3 and _P'4 can be determined in the same manner as _P3 and _P4 in the second negative electrode active material described above.

The first negative electrode active material preferably has a discharge capacity of 100 mAh/g or more at a potential of 1.4 V (vsLi ⁺ /Li) or more and 2.0 V (vsLi ⁺ /Li) or less. Similarly, the first negative electrode active material preferably has a charging capacity of 100 mAh/g or more at a potential of 2.0 V (vsLi ⁺ /Li) or less and 1.4 V (vsLi ⁺ /Li) or more. The method of measuring the discharge capacity and charge capacity is the same as the method of measuring the discharge capacity and charge capacity of the second negative electrode active material described above.

The discharge reaction potential and charge reaction potential of the first negative electrode active material are not particularly limited, but are each, for example, 1.0 V (vsLi ⁺ /Li) or more and 2.0 V (vsLi ⁺ /Li) or less.

Specific examples of the first negative electrode active material include Li ₄ Ti ₅ O ₁₂ , Li ₄ TiO ₄ , Li ₂ TiO ₃ , and Li ₂ Ti ₃ O ₇ . Examples of the shape of the first negative electrode active material include particulate. The average particle diameter (D ₅₀ ) of the first negative electrode active material is, for example, 10 nm or more, and may be 100 nm or more. On the other hand, the average particle diameter (D ₅₀ ) of the first negative electrode active material is, for example, 50 μm or less, and may be 20 μm or less. The average particle diameter (D ₅₀ ) can be calculated, for example, by measurement using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM).

3. Negative electrode active material layer The negative electrode active material layer in the present disclosure contains a first negative electrode active material and a second negative electrode active material. The negative electrode active material layer may contain only the first negative electrode active material and the second negative electrode active material, or may contain other negative electrode active materials. The total ratio of the first negative electrode active material and the second negative electrode active material to all the negative electrode active materials contained in the negative electrode active material layer is, for example, 50 volume % or more, and may be 70 volume % or more, and 90 volume % or more. It may be more than volume %.

Further, the ratio of the first negative electrode active material to the total of the first negative electrode active material and the second negative electrode active material is usually 40 volume% or more, may be 50 volume% or more, and may be 60 volume% or more. You can. On the other hand, the ratio of the first negative electrode active material to the total of the first negative electrode active material and the second negative electrode active material is usually less than 100 volume%, may be 99 volume% or less, and may be 90 volume% or less. You can. If the proportion of the first negative electrode active material is too small or too large, the resistance may not be sufficiently reduced. Moreover, it is preferable that the first negative electrode active material and the second negative electrode active material are each uniformly dispersed in the negative electrode active material layer.

The proportion of the negative electrode active material in the negative electrode active material layer is, for example, 30 volume % or more, and may be 50 volume % or more. If the proportion of the negative electrode active material is too small, there is a possibility that the volumetric energy density cannot be improved. On the other hand, the proportion of the negative electrode active material in the negative electrode active material layer is, for example, 80% by volume or less. If the proportion of the negative electrode active material is too large, good electron conduction paths and ion conduction paths may not be formed.

The negative electrode active material layer preferably contains a solid electrolyte. This is because a good ion conduction path is formed. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

The sulfide solid electrolyte includes, for example, Li element, X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S element. Examples include solid electrolytes. Moreover, the sulfide solid electrolyte may further contain at least one of an O element and a halogen element. Examples of the halogen element include F element, Cl element, Br element, and I element. The sulfide solid electrolyte may be glass (amorphous) or glass ceramics. Examples of the sulfide solid electrolyte include Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ S ₅ , LiI-LiBr-Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ and Li ₂ S-P ₂ S ₅ -GeS ₂ .

The negative electrode active material layer may contain only an inorganic solid electrolyte as the solid electrolyte. Further, the negative electrode active material layer may or may not contain an electrolytic solution (liquid electrolyte). Further, the negative electrode active material layer may or may not contain a gel electrolyte. Further, the negative electrode active material layer may or may not contain a polymer electrolyte.

The negative electrode active material layer preferably contains a conductive material. Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). .

The negative electrode active material layer may contain a binder. Examples of the binder include fluoride binders, polyimide binders, and rubber binders. Further, the thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less. The negative electrode active material layer is used in all-solid-state batteries. Details of the all-solid-state battery will be described later.

B. All-solid-state battery FIG. 4 is a schematic cross-sectional view illustrating an all-solid-state battery in the present disclosure. The all-solid-state battery 10 shown in FIG. It has a positive electrode current collector 4 that collects current from layer 1 and a negative electrode current collector 5 that collects current from negative electrode active material layer 2 . The negative electrode active material layer 2 is the layer described in "A. Negative electrode active material layer" above.

According to the present disclosure, since it has the above-described negative electrode active material layer, it is possible to provide an all-solid-state battery with low resistance.

1. Negative Electrode Active Material Layer The negative electrode active material layer in the present disclosure is the same as that described in "A. Negative Electrode Active Material Layer" above, so the description here will be omitted.

2. Cathode Active Material Layer The cathode active material layer in the present disclosure is a layer containing at least a cathode active material. Further, the positive electrode active material layer may contain at least one of a conductive material, a solid electrolyte, and a binder, if necessary.

Examples of the positive electrode active material include oxide active materials. Examples of oxide active materials include rock salt layered active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , Li _{4 Examples} include spinel type active materials such _{as Ti5O12} and Li( _Ni0.5Mn1.5 ) _O4 , and olivine type active materials such as _LiFePO4 , _LiMnPO4 , _LiNiPO4 , and _LiCoPO4 .

A protective layer containing a Li ion conductive oxide may be formed on the surface of the oxide active material. This is because the reaction between the oxide active material and the solid electrolyte can be suppressed. Examples of the Li ion conductive oxide include LiNbO ₃ . The thickness of the protective layer is, for example, 1 nm or more and 30 nm or less. Furthermore, for example, Li ₂ S can also be used as the positive electrode active material.

Examples of the shape of the positive electrode active material include particulate. The average particle diameter (D ₅₀ ) of the positive electrode active material is not particularly limited, but is, for example, 10 nm or more, and may be 100 nm or more. On the other hand, the average particle diameter (D ₅₀ ) of the positive electrode active material is, for example, 50 μm or less, and may be 20 μm or less.

Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). .

The solid electrolyte and binder used in the positive electrode active material layer are the same as those described in "A. Negative electrode active material layer" above, so their descriptions are omitted here. The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

3. Solid Electrolyte Layer The solid electrolyte layer in the present disclosure is a layer that is disposed between the positive electrode active material layer and the negative electrode active material layer and contains at least a solid electrolyte. The solid electrolyte layer preferably contains a sulfide solid electrolyte as the solid electrolyte. Moreover, the solid electrolyte layer may contain a binder. The solid electrolyte and binder used in the solid electrolyte layer are the same as those described in "A. Negative electrode active material layer" above, so description thereof will be omitted here. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

4. All-Solid Battery The all-solid battery in the present disclosure typically includes a positive electrode current collector that collects current from a positive electrode active material layer, and a negative electrode current collector that collects current from a negative electrode active material layer. Examples of the shape of the positive electrode current collector and the negative electrode current collector include a foil shape. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, and carbon. Moreover, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon.

The all-solid-state battery according to the present disclosure has at least one, and may have two or more, power generation units each having a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer. When an all-solid-state battery has a plurality of power generation units, they may be connected in parallel or in series. The all-solid-state battery in the present disclosure includes an exterior body that houses a positive electrode current collector, a positive electrode material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector. Although the type of the exterior body is not particularly limited, examples thereof include a laminate exterior body.

The all-solid-state battery according to the present disclosure may include a restraining jig that applies a restraining pressure to the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer along the thickness direction. By applying confining pressure, good ion conduction paths and electron conduction paths are formed. The confining pressure is, for example, 0.1 MPa or more, may be 1 MPa or more, or may be 5 MPa or more. On the other hand, the confining pressure is, for example, 100 MPa or less, may be 50 MPa or less, or may be 20 MPa or less.

The all-solid battery in the present disclosure is typically an all-solid lithium ion secondary battery. Applications of all-solid-state batteries are not particularly limited, but include, for example, power sources for vehicles such as hybrid cars, electric cars, gasoline cars, and diesel cars. In particular, it is preferably used as a power source for driving a hybrid vehicle or an electric vehicle. Further, the all-solid-state battery according to the present disclosure may be used as a power source for a moving body other than a vehicle (for example, a railway, a ship, an aircraft), and may be used as a power source for an electrical product such as an information processing device.

Note that the present disclosure is not limited to the above embodiments. The above-mentioned embodiments are illustrative, and any configuration that has substantially the same technical idea as the claims of the present disclosure and provides similar effects is the present invention. within the technical scope of the disclosure.

[Example 1]
(Preparation of negative electrode)
As raw materials, Li ₄ Ti ₅ O ₁₂ (LTO) particles, TiNb ₂ O ₇ (TNO) particles, sulfide solid electrolyte, vapor grown carbon fiber, PVdF binder, and butyl butyrate were prepared, and these were dispersed using ultrasonic waves. A negative electrode slurry was obtained by stirring with a device. The volume ratio of each raw material in the negative electrode slurry is LTO particles: TNO particles: sulfide solid electrolyte: vapor grown carbon fiber: PVdF binder = 53.7: 6.0: 32.2: 2.5: 5. It was set at 6. Note that the volume ratio of LTO particles and TNO particles is LTO particles:TNO particles=90:10. The obtained negative electrode slurry was applied onto a Ni foil as a negative electrode current collector by a blade method, and dried on a hot plate at 100° C. for 30 minutes. Thereby, a negative electrode having a negative electrode current collector and a negative electrode active material layer was obtained.

(Preparation of positive electrode)
As raw materials, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (positive electrode active material), sulfide-based solid electrolyte, vapor grown carbon fiber, PVdF-based binder, and butyl butyrate were prepared, and these were subjected to ultrasonication. A positive electrode slurry was obtained by stirring with a dispersion device. The volume ratio of each raw material in the positive electrode slurry was positive electrode active material: sulfide solid electrolyte: vapor grown carbon fiber: PVdF binder = 66.5:28.5:3.7:1.4. The obtained positive electrode slurry was applied onto an Al foil as a positive electrode current collector foil by a blade method, and dried on a hot plate at 100° C. for 30 minutes. Thereby, a positive electrode having a positive electrode current collector and a positive electrode active material layer was obtained.

(Preparation of solid electrolyte layer)
A sulfide-based solid electrolyte, a PVdF-based binder, and butyl butyrate were prepared as raw materials, and a solid electrolyte slurry was obtained by stirring these with an ultrasonic dispersion device. The weight ratio of each raw material in the solid electrolyte slurry was sulfide solid electrolyte:PVdF binder=99.4:0.4. The obtained solid electrolyte slurry was applied onto an Al foil by a blade method, and dried on a hot plate at 100° C. for 30 minutes. As a result, a solid electrolyte layer (a solid electrolyte layer that can be peeled off from the Al foil) was obtained on the Al foil.

(Production of all-solid-state battery)
The positive electrode active material layer and the solid electrolyte layer in the positive electrode were opposed to each other and pressed using a roll press under conditions of a pressing pressure of 50 kN/cm and a temperature of 160°C. Thereafter, the Al foil was peeled off from the solid electrolyte layer and punched out to a size of 1 cm ² to obtain a positive electrode laminate.

Next, the negative electrode active material layer and the solid electrolyte layer in the negative electrode were opposed to each other, and pressed using a roll press under conditions of a pressing pressure of 50 kN/cm and a temperature of 160°C. Thereafter, the Al foil was peeled off from the solid electrolyte layer to obtain a negative electrode laminate. Further, the solid electrolyte layer in the negative electrode laminate and another solid electrolyte layer were made to face each other and were temporarily pressed using a flat uniaxial press under conditions of a press pressure of 100 MPa and a temperature of 25°C. Thereafter, the Al foil was peeled off from the solid electrolyte layer and punched out to a size of 1.08 cm ² to obtain a negative electrode structure having a solid electrolyte layer and a negative electrode laminate.

The solid electrolyte layer in the positive electrode laminate and the solid electrolyte layer in the negative electrode structure were opposed to each other and pressed using a flat uniaxial press under conditions of a press pressure of 200 MPa and a temperature of 120°C. As a result, an all-solid-state battery was obtained.

[Example 2]
The volume ratio of each raw material in the negative electrode slurry was as follows: LTO particles: TNO particles: sulfide solid electrolyte: vapor growth carbon fiber: PVdF binder = 41.8:17.9:32.2:2.5:5. An all-solid-state battery was obtained in the same manner as in Example 1, except that Example 6 was used. Note that the volume ratio of LTO particles and TNO particles is LTO particles:TNO particles=70:30.

[Example 3]
The volume ratio of each raw material in the negative electrode slurry was as follows: LTO particles: TNO particles: sulfide solid electrolyte: vapor growth carbon fiber: PVdF binder = 29.85:29.85:32.2:2.5:5. An all-solid-state battery was obtained in the same manner as in Example 1, except that Example 6 was used. Note that the volume ratio of LTO particles and TNO particles is LTO particles:TNO particles=50:50.

[Example 4]
The volume ratio of each raw material in the negative electrode slurry was as follows: LTO particles: TNO particles: sulfide solid electrolyte: vapor growth carbon fiber: PVdF binder = 23.9:35.8:32.2:2.5:5. An all-solid-state battery was obtained in the same manner as in Example 1, except that Example 6 was used. Note that the volume ratio of LTO particles and TNO particles is LTO particles:TNO particles=40:60.

[Comparative example 1]
The volume ratio of each raw material in the negative electrode slurry is as follows: LTO particles: TNO particles: sulfide solid electrolyte: vapor grown carbon fiber: PVdF binder = 59.7:0:32.2:2.5:5.6. An all-solid-state battery was obtained in the same manner as in Example 1 except for the above. Note that the volume ratio of LTO particles and TNO particles is LTO particles:TNO particles=100:0.

[Comparative example 2]
The volume ratio of each raw material in the negative electrode slurry is as follows: LTO particles: TNO particles: sulfide solid electrolyte: vapor grown carbon fiber: PVdF binder = 0:59.7:32.2:2.5:5.6. An all-solid-state battery was obtained in the same manner as in Example 1 except for the above. Note that the volume ratio of LTO particles and TNO particles is LTO particles:TNO particles=0:100.

[Comparative example 3]
The volume ratio of each raw material in the negative electrode slurry was determined as follows: LTO particles: TNO particles: sulfide solid electrolyte: vapor grown carbon fiber: PVdF binder = 17.9:41.8:32.2:2.5:5. An all-solid-state battery was obtained in the same manner as in Example 1, except that Example 6 was used. Note that the volume ratio of LTO particles and TNO particles is LTO particles:TNO particles=30:70.

[evaluation]
The all-solid-state batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were sandwiched between two restraining plates and restrained by a fastener at a restraining pressure of 5 MPa. Thereafter, constant current charging was performed at 1/10C to 2.9V, and then constant voltage charging was performed at 2.9V to a final current of 1/100C. Further, constant current discharge was performed at 1/10C to 1.5V, and then constant voltage discharge was performed at 1.5V to a final current of 1/100C. The constant current discharge capacity and the constant voltage discharge capacity up to 1.5V were summed to determine the discharge capacity.

In addition, the SOC of the constrained all-solid-state battery was adjusted by performing initial charging (constant current charging) at 1/10C so that the battery became 50% of the above-mentioned discharge capacity. Using the adjusted all-solid-state battery, a current of 8 mA/cm ² was passed for 10 seconds, and the resistance value was determined by dividing the voltage change before and after that by the current value. The results are shown in Table 1 and FIG. 5.

As shown in Table 1 and FIG. 5, it was confirmed that Examples 1 to 4 had lower resistance than Comparative Example 1 (LTO particles only). Here, since Comparative Example 2 (TNO particles only) has a higher resistance than Comparative Example 1 (LTO particles only), it was expected that the resistance would increase as the proportion of TNO particles increased, but unexpectedly It was confirmed that Examples 1 to 4 had lower resistance than Comparative Example 1. Furthermore, it is presumed that in Comparative Example 3, the resistance was higher than in Comparative Example 1 because the proportion of TNO particles was too large. In this way, by using TNO particles together with LTO particles and by controlling the proportion of LTO particles within a predetermined range, it was possible to reduce the resistance.

1...Positive electrode active material layer 2...Negative electrode active material layer 3...Solid electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...All-solid-state battery

Claims (3)

A negative electrode active material layer used in an all-solid-state battery,
Containing a first negative electrode active material , a second negative electrode active material and an inorganic solid electrolyte ,
The first negative electrode active material, the second negative electrode active material, and the inorganic solid electrolyte are uniformly dispersed in the negative electrode active material layer,
The first negative electrode active material is Li ₄ Ti ₅ O ₁₂ ,
The second negative electrode active material is TiNb ₂ O ₇ ,
A negative electrode active material layer, wherein a ratio of the first negative electrode active material to the total of the first negative electrode active material and the second negative electrode active material is 40 volume % or more and 90 volume % or less . The negative electrode active material layer according to claim 1, wherein the ratio of the first negative electrode active material to the total of the first negative electrode active material and the second negative electrode active material is 50 volume % or more and 70 volume % or less. An all-solid-state battery comprising a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer,
An all-solid-state battery, wherein the negative electrode active material layer is the negative electrode active material layer according to claim 1 or 2 .

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